Fuel cells are known in the art. The fuel cell is an electrochemical device which reacts hydrogen, and oxygen, which is usually supplied from the ambient air, to produce electricity and water. The basic process is highly efficient and fuel cells fueled directly by hydrogen are substantially pollution free. Further, since fuel cells can be assembled into stacks of various sizes, power systems have been developed to produce a wide range of electrical power output levels and thus can be employed in numerous applications.
Fuel cell power systems which need an energy buffer for occasional load surges can utilize batteries to supply energy needs which exceed the energy production capacity of a fuel cell. The output of one of more fuel cells can be coupled to one or more batteries, which provide energy storage for handling temporary load surges.
A typical battery will have different voltage ranges depending on the state of charge of the batteries. Similarly, a battery will charge at a different rate depending on the voltage of the battery when power is flowing into it. Careful management of the state of charge of a battery is important to insure long battery life and optimal battery performance.
In a fuel cell power system, fuel cells produce power, a load will consume power, and a battery will act as a temporary energy buffer. Because the current-voltage curve of a fuel cell can vary widely with load, the output voltage of a fuel cell may not be well-matched to the battery voltage in many instances.
In addition, it is important to prevent fuel cells from overloading by pulling the voltage of a fuel cell too low at high power draw. A further problem is a need to provide DC to DC conversion to a commercially useful voltage. More particularly, fuel cells may produce a voltage that is too low for industrial application, and DC to DC conversion to a higher voltage is desirable.
The invention described below seeks to overcome these problems.